This invention relates to an antenna assembly, and its method of construction. It is particularly suitable for use with portable telecommunications devices such as portable radio telephones.
Recently, advances in miniaturisation technology have enabled smaller and smaller portable radio telephones to be produced. In particular, more efficient electronics have enabled lower-powered batteries to be used, and in conjunction with improved battery technology, it is now possible to produce portable radio telephones which can easily be carried unobtrusively about the person.
An area of telephone technology which has not benefited so greatly from miniaturisation is antenna design. Generally, an antenna has to be a certain size in order to function adequately. This has made it difficult if not impossible for antennas to shrink at the same rate as other elements of portable radio telephones.
Traditional antenna solutions have taken the form of extendible whip or rod antennas which may be withdrawn from the body of the telephone for use, or helical antennas which are smaller than an extended rod antenna, but which permanently protrude from the telephone.
According to a first aspect of the present invention, there is provided an antenna assembly for a telecommunication apparatus, comprising: a conductive element defining a planar antenna; and a tapered and tongue-shaped flexible member arranged to carry the conductive element.
According to a second aspect of the present invention, there is provided an antenna assembly for a communication device comprising a tapered and tongue-shaped flexible member carrying a conductive track in a generally planar equilibrium configuration.
Recently, internal planar antennas have become feasible, but as telephones become ever smaller, the effectiveness of the antenna in both transmit and receive modes can be reduced by the antenna being concealed by the user""s hand.
Therefore, as the bodies of portable radio telephones become smaller, external antenna assemblies become increasingly out of proportion, and internal antennas cannot function as efficiently.
Advantageously, the present invention enables better antenna performance from a given volume of antenna than other antenna structures such as helices and rod antennas. Being flexible, it is also resistant to damage caused by rough handling.
The antenna element may take several forms. It may be produced by selectively bending and shaping a suitable wire, such as stainless steel or spring steel wire. Alternatively, the antenna pattern may be produced by stamping out a suitable pattern from a planar sheet of steel.
Preferably the antenna element is embedded in the flexible member. This protects the potentially delicate antenna from damage.
The flexible member is preferably tongue-shaped, flat and planar, and the flexible member is configured so that the antenna is held in a generally planar equilibrium. This ensures that the antenna is flexible enough to avoid damage caused by rough handling, but the position is stable so that consistent performance can be attained.
Preferably the antenna is disposed on a substrate. This may be achieved by etching techniques as used to produce PCBs, or by printing the antenna onto the substrate using a conductive ink.
An advantage of carrying the antenna on a substrate is ease of handling, and prevention of damage to the antenna element during subsequent operations.
In order to alleviate the problems of compressive and tensile forces acting on the antenna element when the flexible member bends, it is preferable to dispose the antenna along the midpoint or central bend axis of the flexible member. In this way, the potentially damaging forces have the least effect. This is desirable whether the antenna is disposed on a substrate or not.
In the case when the antenna is disposed on a substrate, it is preferable to sandwich the antenna element between its substrate and another similarly dimensioned piece of substrate material, to ensure that the antenna is disposed on the central bend axis.
In order to maximise the bond between the two halves of the flexible member when a substrate is used, it is preferable to provide one or more apertures in the substrate so that cohesive bonding can occur between the portions of material providing the flexible member. If two layers of substrate are used, then both layers can be perforated.
The antenna assembly preferably comprises a rigid base member to facilitate attachment to a telecommunication apparatus. This base member also provides a means for electrical connection of the antenna.
Some suitable materials for the various parts of the antenna assembly are:
Substrate: Polyester
Flexible member: Thermo plastic elastomer
Rigid Base Member: Glass Filled (10-15%) Polypropylene.
According to a third aspect of the present invention, there is provided a method of producing an antenna assembly comprising the step of: encapsulating a planar antenna element within a flexible member.
Preferably, the antenna is first disposed on a substrate.
Injection moulding techniques are preferably employed to overmould each side of the substrate so that the entire substrate is encapsulated, except for a small portion which allows for electrical connection to the antenna.
Preferably, the overmoulding on each side extends slightly beyond the outer edge of the substrate to ensure that cohesive bonding occurs between the two portions of the flexible member. This advantageously provides a good seal around the antenna assembly.